I plan on trying to engrave black acrylic sheet with a 445nm diode. One thing I was thinking about, since the surface of the sheet is pretty shiny, do I have to worry about the laser reflecting off of it? Or since it's black will it mostly absorb?

I'm trying to engrave grooves for a project I'm working on, that requires grooves of a v-shape. I was told it should do the trick. I need as clean of grooves as possible. I'm using a 445 diode because of advice someone on this forum gave me. What would be a better way to do it on a hobbyist budget? I already have a 445 and g2 lens on the way from DTR

You won't achieve precise groove profile. Laser will burn the plastic. Most simple plastics will just dissolve mostly into CO2 and H2O. It will leave round groove with elevated borders, as the plastic will only melt a bit on the borders.
You can cut through rather cleanly. You can leave visible marks on surface easily. But I have no idea how to achieve well defined V groove profile.

I dunno if a 405nm diode will even cut acrylic, and if it does, it'll be extremely slow. What thickness are you talking about? I use a 40W CO2 laser to cut acrylic, and for only 3mm thick I have to run it at about 10mm/s.

Yes! That is the idea. Not sure if I can pull it off, but I've heard that there's someone in Europe that has succeeded in doing this, so I thought I'd give it a try. Not sure if acrylic is the correct material to use, but I sure as hell don't want to use PVC.

If I fail at doing this, at least I'll still have an awesome laser to mess with

I could imagine it would more or less work with mono .. but as I said - you would have no control over the geometry of the groove. It's worth trying, even mono might be fun. And I think 405 would be enough. You might not be able to record in real time, but who cares. As long as you have some cheap spare heads (or how do you call it in English).